Have a look and see if there is any tape in the channel. There "should be". Heat up the outside with a hair dryer and slowly pull the channel away from the glass. You might find three pieces of self adhesive felt. It is really easy to heat up the adhesive.

I would probably be inclined to let the backglass warm up to normal temperature before putting heat on it with the hairdryer.

I have heard  of stories of BG's shattering just from the warmth of your fingers especially on these cold winter mornings.